1. The Field of the Invention
This invention relates to the field of communication cable technology. More specifically, this invention relates to a cable made of wire pairs. Additionally and more specific, this invention relates to a communication cable for facilitating propagation of high frequency signals with minimal interference to adjacent signals within a multiconductor cable.
2. Relevant Technology
Traditional interface cables have heretofore assumed a largely parallel environment which also heretofore has provided adequate signal propagation for traditional audio frequencies. However, with the advent of high fidelity audio equipment in addition to the ubiquitous nature of high frequency and even high bandwidth computer and other communication devices, a largely planar and parallel orientation of interconnection wires has proven inadequate as the rise times, and hence the frequencies associated therewith, have increased to levels which induce the propagation of signals that can and do provoke distortion and interference into adjacent conductors.
One interim attempt at remedying such cross-talk has been to employ a cable having a center conductor with a dielectrically-interspersed sheathed shielded conductor. Such cabling attempts have commonly become known as coaxial cable (hereinafter "coax" cable). Standard coax cable has heretofore been used for sensitive-signal connections ranging from audio frequencies to several megahertz signals. However, as alluded to hereinabove, with the advent of higher frequency intercommunications, the increased rise times as well as the augmented bandwidth capabilities, now extending into the gigahertz frequencies, previous cable designs have been rendered inferior, inadequate and even obsolete. Those skilled in the art of cabling technology appreciate that coax cabling has at least two major inherent defects that become more pronounced at high frequencies and faster digital signal rise times.
First, typical coax cabling incorporates an outside conductor to shield the inner conducting lead using what may be thought of as a "Faraday Shield" for protecting the inner conductor from any outside signal interference. However, while the outer conductor shields the inner conductor from exterior extraneous signals, the inner conductor radiates its preferred signal into the shield or outside conductor which mixes with the outside-induced signals. Such a mixing or combining has heretofore been overlooked or ignored since they were previously considered only tolerable at their then present levels. One of the particularly overlooked facts has been that such signals cause random currents to be set up in the outside "shield" conductor which causes, over the length of the cable, a more predominant direct current (DC) voltage offset. Such a DC offset causes a DC shift in the timing edge of digital circuits since the signals induced in the outside conductor are alternating in response to the preferred signal projections from the inner conductor as well as the ambient signal levels exterior to the cable assembly, they tend to cause the DC offset voltage to vary with the induced noises and the primary signal.
A second shortcoming with a coax cabling system is that a coax system is not a balanced cabling system and coax only has a very limited frequency range where the Z.sub.0 impedance is consistent with the rated impedance. Therefore, out-of-cable-specification signals cause an imbalance which causes reflected energy to be set up thereby requiring some form of electrical correction to subdue the reflected energies.
Thus, what is needed is a cable assembly capable of operating over a broad frequency range without incurring the shortcomings of the prior implementations.